In spacecraft, the MIL-BUS 1553B communication bus is used by the on-board computer for the control and monitoring of the spacecraft's platform and payload. The implementation of this bus is bulky, power consuming and limited in the number of terminals that can be attached to the bus. With increasing complexity of spacecraft, the number of units on the platform and payload to be controlled increases for a decreasing weight and power budget. These new requirements can be met by the Controller Area Network (CAN) bus, which has been developed for automotive control applications. The CAN bus communication protocol has been used in several spacecraft mainly in low earth orbits with the communication physical layer implemented with up-screened commercial CAN transceivers. For geostationary orbits, which present a harsher radiation environment, a radiation tolerant transceiver is required.
Further, conventional CMOS processes are not optimized for high current throughput as would be required for a CAN transceiver, which results in a high voltage drop between the supply voltage level and the differential dominant output voltage level. For instance, for a 3V supply voltage level, it would be difficult to even attain a 1.5V differential dominant output voltage level.
In addition, unlike the MIL-BUS 1553B bus that is used between units and is limited to 30 nodes, the CAN bus can have in excess of 100 nodes from inter and intra equipment units. The addition of sub-branches on the bus can increase this number ten to hundred fold. For such number of interfaces, the conventional approach of using a separate transceiver to translate the CMOS signal from the CAN controller to the CAN bus levels is no longer feasible and efficient integration of the transceiver with the digital should be sought. This implies that instead of using a special high-voltage analog CMOS process to meet the CAN electrical and radiation requirements for the transceiver, a digital CMOS process, as also used for the CAN controller, should be used. However, these radiation tolerant digital processes have not been optimized for high voltage capability.
Thus, there is a need for a transceiver for a differential signaling bus that does not suffer from high voltage drop between the supply voltage level and the dominant differential voltage level. There is a further need for a radiation tolerant transceiver. There is a yet further need for a radiation tolerant and high voltage tolerant transceiver.